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Real-Time Monitoring of Active Landslides

When do landslides turn catastrophic?

Reducing Landslide Hazards in the United States

Real-Time Monitoring of Active Landslides


Landslides threaten lives and 

property in every State in the 

Nation. To reduce the risk from 

active landslides, the U.S. 

Geological Survey (USGS) develops 

and uses real-time landslide monitoring systems. Monitoring can 

detect early indications of rapid, 

catastrophic movement. 

Up-to-the-minute or real-time 

monitoring provides immediate 

notification of landslide activity, 

potentially saving lives and property. 

Continuous information from 

real-time monitoring also provides 

a better understanding of landslide 

behavior, enabling engineers to 

create more effective designs for 

halting landslide movement. 

During heavy rains in January 1997, 

thousands of tons of earth gave way in 

the Sierra Nevada, destroying three homes, 

blocking a major northern California highway (U.S. 50), and briefly damming the 

adjacent American River. Waters dammed 

by the landslide quickly flooded two vehiMassive landslide that blocked Highway 50 and 

temporarily dammed the South Fork of the American 

River (Photo: Lynn Harrison, Caltrans) 

Homes destroyed by a sudden catastrophic landslide in 1997 along U.S. Highway 50, about 25 miles east of 

Placerville, California (Photo: Mark Reid, USGS) 

cles traveling on the highway, leading to 

dramatic rescues. Reopening the highway 

cost $4.5 million, and indirect economic 

losses from the highway closure exceeded 

$50 million. 

Several large, active landslides in the same 

area continue to threaten U.S. Highway 50. 

Although these slides often move slowly, 

some have the potential to collapse catastrophically. To help reduce the risk posed 

by these landslides, the USGS, in cooperation with other agencies, acted quickly to 

provide continuous real-time monitoring of 

landslide activity using systems developed 

by the USGS for monitoring active volcanoes in remote areas. Data from a variety of 

sensors installed at the landslides are transmitted by radio to USGS computers. Graphs 

of sensor response are available over the 

Internet to local officials, geotechnical engineers, and emergency managers. 

Why is it necessary to collect real-time 

landslide data remotely? The immediate 

detection of landslide activity provided by 

When do landslides turn catastrophic?


Many landslides are inactive during dry times 

and move only during or following extended 

periods of infiltration from rain or melting snow. 

Increased water pressure in the ground reduces 

the overall strength of hillsides and starts 

downslope movement, but landslide speed and 

potential destructiveness can vary widely. Some 

landslides move slowly, traveling only a few 

inches in many days. Other landslides can 

transform suddenly into mud or debris flows that 

travel thousands of feet in a matter of minutes, 

cause massive destruction, and kill people. 

Monitoring can determine the speed of landslide 

movement and can also detect early indications 

of catastrophic movement. Rapid movement at 

some landslides, for example, is preceded by 

gradual acceleration. Using real-time data from 

such slides, geologists can anticipate possible 

catastrophic movement. USGS landslide monitoring focuses on detecting (1) precipitation and 

ground-water conditions that could destabilize a 

hillslope, (2) acceleration of slide movement, and 

(3) ground vibrations associated with movement. 

U.S. Department of the Interior 

U.S. Geological Survey U.S. Geological Survey Fact Sheet 091-99 
For more information:

Current USGS remote landslide monitoring sites in the 

western United States (number indicates number of 

sensors in each area) 

real-time systems can be crucial in saving 

human lives and protecting property. 

Traditional field observations, even if taken 

regularly, cannot detect changes at the 

moment they occur. Moreover, active landslides can be hazardous to work on, and 

large movements often occur during storms 

when visibility is poor. The continuous data 

provided by remote real-time monitoring 

permits a better understanding of dynamic 

landslide behavior that, in turn, enables 

engineers to create more effective designs to 

prevent or halt landslides. 

At landslide areas remotely monitored by 

the USGS, ground movement and groundwater pressures are measured every second. 

The amount of downslope movement is 

recorded by extensometers that can detect 

stretching or shortening of the ground. 

Ground vibrations caused by slide movement are monitored by geophones buried 

within the slides. Ground-water conditions 

within the slides are monitored by porewater-pressure sensors, and on-site rain 

gauges record precipitation. Under normal 

Network for transmission of real-time landslide data 

conditions, data are transmitted to USGS 

computers every 10 minutes, but data are 

transmitted immediately if strong ground 

vibrations caused by massive landslide 

movement are detected. 

Currently, five landslides along U.S. 

Highway 50 are monitored in real-time using 

58 instruments. This network, operated in 

cooperation with the California Department 

of Transportation, provides engineers and 

geologists with early notification of landslide 

activity and with information useful in the 

design of remedial measures to halt these 

slides. Real-time data from one of these 

landslides is available to the public over the 

Internet at 

http://landslides.usgs.gov/hwy50. 

Above: Testing a solar-powered radio telemetry system 

for remote transmission of real-time landslide data 

(Photo: Mark Reid, USGS) 

Right: Measuring landslide movement using an 

extensometer (an instrument that can detect stretching of the ground surface between stable ground and 

sliding ground) (Photo: Richard LaHusen, USGS) 

The USGS operates other remote real-time 

landslide monitoring sites. Near Seattle, 

Washington, a real-time system monitors a 

slide threatening a major railway 

(http://landslides.usgs.gov/woodway), and in 

Rio Nido, California, another system monitors a large landslide threatening more than 

140 homes. Remote monitoring by the 

USGS in Fremont, California, detects landslide movement threatening downslope 

homes, and in New Mexico, remote monitoring records the effects of wildfire in 

destabilizing hillslopes. In Colorado, remote 

monitoring at several landslide sites provides notification of ground movement 

caused by large slow landslides or by rapid 

debris flows. 

Active ground movement, including landsliding, occurs in every state in the 

Nation. To help reduce the risk from landslide hazards, scientists at the USGS have 

developed real-time monitoring and other 

tools that help in understanding and predicting where, when, and how landslides occur. 

USGS scientists also provide technical 

assistance to local authorities during landslide disasters. The work of the USGS 

Landslide Hazards Program is helping to 

protect people's lives and property from 

landslide hazards throughout the United 

States. 

Mark E. Reid 

Richard G. LaHusen 

William L. Ellis 

Cooperating Organizations 

California Department of Transportation


California Division of Mines and Geology


California Office of Emergency Services


City of Fremont, California


Colorado Department of Transportation


Colorado Geological Survey


Federal Emergency Management Agency


Garfield County, Colorado


National Park Service


Pitkin County, Colorado


Sonoma County, California


U. S. Bureau of Land Management


U. S. Department of Agriculture, 


Forest Service


For more information: 

National Landslide Information Center 

U.S. Geological Survey, Federal Center 

Box 25046, MS 966, Denver, CO 80225 

1-800-654-4966 

http://landslides.usgs.gov 

NLIC@usgs.gov 

Real-time monitoring: 

http://landslides.usgs.gov/hwy50 

http://landslides.usgs.gov/woodway